Our aims over the past 6 years has been to examine the effects of high altitude on growth of the lungs and thorax and of mechanical stress (left pneumonectomy) on growth of the remaining lung in Beagle dogs. We have already measured lung pressure volume relationships, pulmonary diffusing capacity for CO, capillary blood flow, tissue volume and pulmonary hemodynamics in 6 groups of Beagles; 3 groups in which interventions were performed as adults and 3 in which interventions were performed as puppies. A. Intervention as Adults: 1. Six Adult Beagles raised at sea level and taken at age 24 months to 10,000 feet for 3 years. 2. Six Adults Beagles of the same age kept simultaneously at sea level. 3. Six Adult Beagles of the same age kept at sea level and left pneumonectomy performed at age 54 months. B. Intervention as Puppies. 1. Six Beagles, born at sea level and raised from puppies at 10,1000 feet from age 2 months until age 18 months. 2. Six control Beagles raised simultaneously at sea level. 3. Six Beagles raised at sea level after left pneumonectomy at age 2 months. All Beagles have been sacrificed after thoracic CT scans and the lungs fixed inflated with gluteraldehyde. Carcasses are frozen and will be skeletonized by dermestid beetles. The left diaphragm was fixed in situ by gluteraldehyde perfusion and the right frozen. Present aims are measurements of: 1. Alveolar number, surface area and quantity of arterial smooth muscle. 2. Skeletal morphometry of thoracic cage, skull and long bones. 3. Thoracic dimensions and relative amounts of fat in thoracic wall from CT scans. 4. Fiber types, oxidative potential and capillarity of respiratory muscles.